Floor surfacing machine



March 16, 1948. w. E. HOLT 2,437,958

FLOOR SURFACING MACHINE Filed March 14, 1942 IN VENT OR.

29. "Wm-m E. Holt ATTORNEY Patented Mar. 16, 1948 UNITED STATES PATENT orncs FLOOR SURFACING MACHINE William E. Holt, Oakland, Calif.

Application March 14, 1942, Serial No. 434,677

8 Claims. 1

My present invention relates in general to the construction and maintenance of floor surfacing machines. Such machines comprise a surfacing element, such as a rotary drum, having its outer .surface or periphery covered by a sheet of abrasive material. Between the sheet of abrasive material and the peripheral surface of the drum is ordinarily interposed a layer of cushioning material, such as felt or sponge rubber, secured to the drum. In view of the necessity of frequently replacing the sheet of abrasive material, the drum and layer of cushioing material are usually formed with registering transverse slots into which the opposite ends of the abrasive sheet fit and are clamped into position.

The drum must be perfectly balanced for efficient operation and in order to maintain this balanced condition when in use, the layer of cushioning material must be securely held in position relative to the drum periphery. Detachably connecting the layer of cushioning material to the drum at circumferentially spaced points while theoretically highly desirable from the standpoint of facilitating replacement thereof is practically undesirable because of the unbalancing of the drum due to distortion or movement of the cushioning material between the points of connection under the tangential and centrifugal stresses imposed thereon in use, and the relatively low shear strength of the cushioning material, preventing the use of ordinary fastening means. For the foregoing reasons, the cushioning material is cemented substantially throughout its extent to the periphery of the drum.

In use, the abrasive sheets are frequently split or ruptured exposing a portion of the cushioning material to direct contact with and abrasion by the floor surface. Such damaging of the cushioning material tends to throw the drum out of balance and subsequent use of the cushioning-material in this condition would cause chatter marks on the floor surface. The layer of cushioning material is also frequently ruptured in operation, requiring its replacement.

The present practice of installing or replacing the layer of cushioning material, such as a sheet of sponge rubber, is to first remove the drum from the machine and thoroughly clean the periphery thereof with a cleaning fluid. The rubber sheet is then cut to approximately the desired size and shape and a coating of cement applied to one side. The rubber sheet is then firmly taped around the drum with the cement in contact with the drum and allowed to set for about twenty-four hours. The tape is then removed and the rubber sheet trimmed to the proper size. Rebalancing of the drum is frequently required after this operation. The foregoing operations are necessary each time the cushioning material requires replacement and as skilled labor is preferable, the drum is usually sent to a service point, preventing the use of the surfacing machine for several days. The expense and inconvenience of such drums replacement operations has been found to substantially restrict the sale of floor surfacing machines in territory where the seller does not maintain convenient servicing points, thus requiring the maintenance of a large servicing organization or substantially restricting such sales territory to inferior machines of relatively local manufacture.

When the machine is in use, the layer of abrasive material, such as a sheet of sand paper, on the drum requires frequent replacement. This sheet must beheld tightly around the drum and for this reason the ends of the sheet are inserted into a slot in the drum periphery. The

ends are positioned in a slot formed by the fiat- I tened sides of two oppositely rotated knurled arms within the drum which are then turned to grasp the sheet ends and hold the sheet taut around the drum. When the drum is installed in the machine, it is difiicult to determine when the knurled arms are in the proper position to receive the sheet ends.

The main object of my present invention is the provision of a drum cushioning element which can be quickly and accurately installed on and removed from the drum of a floor surfacing machine by the user at a relatively low cost. A further object is the provision in a floor surfacing machine of a drum construction facilitating the installation and removal of the abrasive sheet without removing the drum from the machine.

The various features of novelty which characterize my invention are pointed'out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

Of the drawings:

Fig. 1 is a perspective view of one type of floor surfacing machine for which my invention is particularly adapted;

Fig. 2 is a perspective view of a surfacing drum assembly incorporating my invention;

F g. 3 is a perspective view of the drum shown 3 in Fig. 2 disassembled and of the abrasive sheet used therewith;

Fig. 4 is a longitudinal section through the drum;

Fig. 5 is an end view of the drum;

Fig. 6 is an enlarged transverse section of one end of the drum;

Fig. '7 is an enlarged view of a portion of Fig. 4; and

Fig. 8 is an end View of the demountaole drum cushion.

In Fig. 1 I have illustrated a floor surfacing or sanding machine of a well known type comprising a wheeled housing IE] enclosing arotary surfacing element ll driven by an electric motor l2 mounted on the housing. The motor also drives an exhaust fan i3 connected to a dust collecting nozzle adjacent the surfacing element H and delivering the dust-laden air through a. combined handle and dust pipe Hi to a dust bag (not shown). A hinged shield is extends across the front of the housing and may be raised from its operating position to permit access to the surfacing element.

The surfacing element H comprises a hollow metal drum formed by a cylindrical plate ll closed at its ends by circular end plates i8 and I9 secured thereto and rigidly mounted on a drive shaft 2| journalled in bearings mounted in opposite side plates of the housing it. The plate I! has a narrow slot 22 extending longitudinally of the drum at an oblique angle to the drum axis. A pair of clamping arms or rolls 23 and 24 are rotatably mounted in the end plates of the drum adjacent the inner end of the slot 22, as shown in Fig. 6. The rolls have a projecting squared end at opposite ends of the drum adapted to .be engaged by suitable tools for turning the rolls. The portion of the rolls within the drum is flattened along one side 26 and the remaining part knurled. The knurled portions of the rolls cooperate to form a clamping means for the tapered ends of a sheet of abrasive material 28, such as a sheet of sanding paper or emery cloth, inserted in the slot formed by the flattened portions. The 1 rolls 23 and 24 are then turned by the operator so as to have the knurled portions grip the opposite ends of the abrasive sheet and draw it tightly around the drum periphery.

To facilitate the positioning of the rolls so that the flattened sides of the rolls will form the slot for receiving the sheet ends, each roll has a circumferential slot 29 in its journalled end portion opposite its squared end. A set screw 33 is mounted in the drum so as to project into each a slot 29. A pin 3| is partly driven into the slotted portion of each roll at a point where it will abut the projecting end of the set screw 39 when the flattened portion of the roll is in line with the corresponding side of the slot 22. Each set screw 33 and pin 31 thus cooperate to serve as a stop positively indicating to the operator the proper position of each roll for the withdrawal and insertion of the ends of the sheet 28. After the sheet ends are positioned between the rolls, the rolls are simultaneously turned in opposite directions, as indicated by the arrows in Fig. 6, until the sheet is gripped by the rolls and drawn tight- 1y around the drum. The machine is then ready for use.

In accordance with my invention the drum is provided with a demountab-le cushioning element. The cushioning element consists of a relatively thin backing sheet, preferably of two substantially semi-cylindrical metallic plates 36 shaped to fit around the periphery of the drum with one pair of straight edges substantially in contact and the oblique opposite edges extending along the oblique edges of the slot 22.

In assembling a cushioning unit, the composite backing sheet is bent around a master drum and a layer of cushioning material 40, preferably a sheet of sponge rubber, conforming in size and shape to the backing sheet is bent around the sheet and securely cemented thereon substantially throughout its extent. The two part construction of the backing sheet facilitates the installation on and removal of the cushioning unit from the drum without removing the drum from the machine, as the cushioning unit can be easily bent into the position indicated in broken lines in Fig. 8 for that purpose.

The drum is constructed to permit the rapid installation and removal of the cushioning unit. For this purpose an annular ring 4| having an inwardly extending circumferential flange 62 is secured by screws 43 to the circular end plate IS with the flange slightly spaced from the pcripheral surface of the drum, so that the corresponding end of the backing plates 35 will fit under the flange. The circular edges of. the plates 36 are beveled, as indicated in Figs. 4 and 7, and adjacent surface of the layer 40 slightly cut away to facilitate positioning of the plates 36 within the flange 42. The opposite edges of the plates are held by a circular plate or retaining chuck 43 having a circumferential inwardly extending flange 44 adapted to fit over the beveled edges of the plates 36 in the same manner as the flange 42, The plate 43 fits over the drive end of the shaft 2| outside the drum end plate I9 and is held in that position by a lock nut 45 threaded on the projecting portion of the drive shaft. Holes 46 are formed in the sides of the lock nut to permit turning thereof by devices, such as a nail set. Short slots 4'! are formed in the circumferential edge portions of the plate 43 to permit a tool to be inserted therein to disengage the flange 44 from the cushioning unit when the lock nut is loosened. The squared end of the roll 23 projects through an arcuate slot 43 in the chuck plate 43, as shown in Fig. 2.

In the original assembly of the cushioning unit and drum, the cushioning unit shown in Fig. 8 is fitted around the drum with its spaced edges aligned with the slot 22. The cushioning unit is then slid longitudinally of the drum until the curved edge portions of the plates 35 fit under the flange 42. The chuck plate 43 is then positioned on the shaft 2| with its flanged edge 44 fitting over the adjacent edges of the plates 36 and the squared end of the roll 23 projecting through the slot 48. The lock nut is tightened to hold the described parts in their assembled position. The drum is then ready for installation in the machine and mounting of the abrasive sheet.

In replacing the cushioning unit. the drum as" sembling operations are reversed except that it is not necessary to remove the drum from the machine, since there is normally suificicnt room between the side plate of the housing and the end of the drum to disengage the lock nut 45 and clutch plate 43 and to move the cushioning unit out of contact with the flange 42 so that it can be bent as indicated in Fig. 8 and removed." When the lock nut is loosened, the chuck plate 43 can be easily pried out of engagement with the cushioning element by inserting a screw driver in the slots 41, The cushioning unit is then forced out from under the flange 42 and quickly replaced by a spare.

With the described construction and operation, the cushioning unit may be easily and quickly re placed when desired by the user, eliminating the expensive and laborious operations heretofore required in such cases. Since the cushioning devices can be made up in standard units for each size of drum, no rebalancing of the drum is required after such a replacement operation.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of my invention now known to me, those skilled in the art will understand that changes may be made in the operations and form of the invention disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a correspondin use of other features.

Iclaim:

1. A replaceable cushioning device for a rotary drum having a cylindrical peripheral surface rovided with a slot arranged lengthwise of and obliquely to the drum axis of rotation, which comprises two substantially semi-cylindrical rela tively thin plates of substantially rigid material forming a two-part backing sheet shaped to fit around the peripheral surface of the drum with spaced oblique plate edge portions conforming with the edges of said slot, and a continuous layer of resilient material shaped to fit around the peripheral surface of said drum and cemented to the outer side of said backing sheet substantially throughout its extent.

2. A replaceable cushioning device for a rotary drum having a cylindrical peripheral surface provided with a slot arranged lengthwise of and obliquely to the drum axis of rotation, which comprises two substantially semi-cylindrical relatively thin metallic plates forming a two-part metallic backing sheet shaped to fit around the peripheral surface of the drum with spaced oblique plate edge portions conforming with the edges of said slot, and a continuous layer of sponge rubber shaped to fit around the peripheral surface of and cemented to the outer side of said backing sheet plates substantially throughout their extent when mounted on said drum.

3. In a floor surfacing machine, the combination of a rotary drum having opposite end walls and a cylindrical peripheral surface provided with a slot extending lengthwise of said drum, cushioning means for the peripheral surface of said drum, a sheet of abrasive material extending around said drum peripheral surface with its opposite ends fitting into said slot, and means in said drum for detachably holding the ends of said abrasive sheet com-prising a pair of parallel knurled rolls journalled in said drum end walls adjacent said slot, said rolls having flattened surface portions cooperating to form a slot therebetween within said drum substantially parallel to said drum slot. tool engaging portions 0n opposite ends of said rolls, and cooperating means on said drum and rolls for limiting the arcuate movement of each roll in one direction at a position wherein the corresponding flattened surface portions cooperate to form said second slot.

4. In a floor surfacing machine, the combination of a rotary drum having opposite end walls and a cylindrical peripheral surface provided with a slot extending lengthwise of said drum, cushioning means for the peripheral surface of said drum, a sheet of abrasive material extending around said drum peripheral surface with its opposite ends fitting into said slot, and -means in said drum for detachably holding the ends of said abrasive sheet comprising a pair of parallel knurled rolls journalled in said drum end walls adjacent said slot and having flattened surface portions cooperating to form a slot therebetween within said drum substantially parallel to said drum slot, tool engaging portions on opposite ends of said rolls, and stop means for limiting the arcuate movement of each roll in one direction at a position wherein the corresponding flattened surface portions are in planes parallel to the sides of said drum slot and cooperate to form said second slot.

5. In a floor surfacing machine, the combination of a rotary drum having opposite end walls and a cylindrical peripheral surface provided with a slot extending lengthwise of said drum, cushioning means for the peripheral surface of said drum, a sheet of abrasive material extending around said drum peripheral surface with its opposite ends fitting into said slot, and means in said drum for detachably holding the ends of said abrasive sheet comprising a pair of parallel knurled rolls journalled in said drum end walls adjacent said slot and having flattened surface portions cooperating to form a slot therebetween within said drum substantially parallel to said drum slot, tool engaging portions on opposite ends of said rolls, and means for limiting the arcuate movement of each roll in one direction at a position wherein the corresponding flattened surface portions cooperate to form said second slot comprising a circumferential groove on each roll, a pin in said roll extending into said groove, and a fixed stop member on said drum arranged to pro ject into said groove.

6. A rotary surfacing element comprising a rotary drum having a slot extending lengthwise of the peripheral surface thereof and obliquely to the drum axis, a cushioning device for said peripheral surface comprising a metallic backing sheet'sectioned along an axial line and shaped to fit around and conform to said peripheral surface and a continuous layer of resilient material cemented to the outer side of said backing sheet substantially throughout its extent, said backing sheet and layer of resilient material having spaced oblique edge portions in line with said drum slot, means on said drum for detachably engaging circular edge portions of said backing sheet for holding said cushioning device in position on said drum, a sheet of abrasive material fitting around said layer of resilient material with its ends extending into said drum slot, and means within said drum for holding the ends of said sheet of abrasive material taut.

7. A rotary surfacing element comprising a rotary drum having a cylindrical peripheral surfaceprovided with a slot arranged lengthwise of the drum axis of rotation, a cushioning device for the peripheral surface of said drum compris= ing a backing sheet of substantially rigid material sectioned along an axial line and shaped to fit around and conform to said peripheral surface and a continuous layer of resilient material cemented to the outer side of said backing sheet substantially throughout its extent, said backing sheet and layer of resilient material having spaced edge portions in line with said drum slot, means for detachably connecting said cushioning device in position on said drum comprising a circumferentially extending flange at one end of and radially spaced from the peripheral surface of said, drum sufliciently to receive the cor-- responding circular edge portion of said. backin sheet between saicl flangeand drum, meansdetaehabiy engaging the opposite circular edge portion of said hacking. sheet, means for holding the parts in assembled; relation, a sheet of abrasive material. fitting: around said layer of resilient material with its ends extending. into said drum slot, and. means within said" drum for holding the ends or said sheet of abrasivematerialtaut.

8. At demountaible cushioning member for a rotary' surfacirrg drum: having a. slot in its peripheral:' surface extending. obliquely to' the drum axis, which comprises a pair of? oppositely arranged substantially semi-cylindrical thin metallic plates havingabutting straight edge portions and spaced edgeportions extending: obliquely to the axis of the cylincler, and a continuous layer of resilient material cemented to the outer sides of said metallie plates substantially throughout their exter'it and having spaced edge portions in line with the obliquely extendin edge: portions as Sara plates. 7

El HOL'I.

REFERENCES? CITED- Tlie following. references are of record. in the fileof this patent:

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